1. Field of the Invention
The present invention relates to a CVD apparatus, and more particularly, to a CVD apparatus intended for forming a Cu thin film, used as a wiring material or the like in semiconductor integrated circuits.
2. Prior Art
In recent years, as there is a tendency for semiconductor devices to be highly integrated, dimensions such as wiring width, wiring spacing and the like in metallic wiring for formation of integrated circuits tend to decrease. Such reduction in wiring dimensions leads to an increase in wiring resistance and also narrowing of wiring spacing leads to an increase in parasitic capacitance between wirings, which causes a problem that time delay of electric signals in integrated circuits increases. In this case, a measure to increase a wiring height to increase a cross sectional area of wiring is taken in order to suppress an increase in wiring resistance but a wiring height cannot be increased excessively because the increase in areas of facing surfaces of wirings leads to the increase in parasitic capacitance. Such problem in time delay of signals has become serious to the extent that the normal operations of integrated circuits are impeded in wiring dimensions of around 0.1 micron.
Also, an increase in resistance and electric current density, due to a reduced wiring width, will cause wiring temperature rise due to Joule heat and electromigration to degrade reliability in integrated circuits.
Hereupon, in order to solve the problems in time delay of signals and degradation of reliability, Cu having a lower resistance and a higher fusing point than those of Al has recently been used as a material for metallic wiring.
Meanwhile, while a three-dimensional wiring construction using a multi-layered wiring is made in semiconductor integrated circuits, the reduction in wiring dimensions involves a tendency for via holes, by which the connection of three-dimensional wiring is made, to become minute. Embedding of Cu by means of electrolytic plating has been made as a method of embedding a metallic material in such minute via holes.
Plating requires a Cu thin film (seed Cu layer), which is formed by means of the sputtering method.
However, there is a problem that when wiring dimensions come to a level of 0.1 micron to lead to an increase in aspect ratio (ratio of hole depth to opening diameter), the seed layer with adequate thickness is not formed on hole walls due to the poor step covering performance of the sputtering method, thus resulting in failure in plating.
With a further increase in the aspect ratio, the failure is caused in embedding in the holes even with the electrolytic plating. The Cu embedding technique by the CVD method (chemical vapor deposition method) has been given attention and investigated in order to solve the problem of embedding of metallic wiring in such minute holes and to afford the formation of even seed layer and complete embedding in interiors of minute holes having an opening diameter of 0.1 micron or less.
With respect to Cu embedding by the CVD method, a study report has been presented to indicate the possibility of complete embedding in minute holes with an aspect ratio of 7 at adequate deposition rate, as described, for example, in Jpn. J. Appl. Phys. Vol. 37 (1998) pp. 6358-6363, and thus the CVD method has been recognized as a promising Cu embedding technique.
As has been described above, techniques with respect to the Cu wiring and embedding are exceedingly important in semiconductor integrated circuits, which will be further promoted in high integration and high performance in the future, and the importance of the CVD method and apparatus intended for formation of Cu thin films is increasingly enhanced in the semiconductor mass-production process.
It is believed that such development of Cu-CVD apparatus in the semiconductor mass-production process is attainable by application of conventional metal CVD apparatuses. Hereupon, examinations have been tried, in which a gas introduction mechanism of the tungsten CVD apparatus currently involving a most established technique as a metal CVD apparatus is modified to suit for a raw material used in the Cu-CVD apparatus.
The gas introduction mechanism in the tungsten CVD method is one, in which vapor of tungsten hexafluoride being a liquid material is introduced into a deposition chamber while being controlled in flow rate by an ordinary gas mass flow controller. Meanwhile, with the Cu-CVD method, organic liquid materials, for example, Cu (hfac) (tmvs) are used as a raw material, but vapor pressure thereof is as low as at most 100 Pa at room temperature, so that ordinary gas mass flow controllers cannot be used. Hereupon, as described, for example, in Jpn. J. Appl. Phys. Vol. 37 (1998) pp. 6358-6363, an introduction method is used, in which a liquid material is fed to an evaporator at a predetermined flow rate with the aid of a liquid mass flow controller and is vaporized in the evaporator, and then is fed to a deposition chamber. Such a raw material gas introduction mechanism composed of the liquid mass flow controller and the evaporator is different from the gas introduction mechanism in the tungsten CVD method.
Besides this, the introduction method uses a gas introduction section for introducing a vaporized gas directly into the deposition chamber, a substrate heating mechanism and an exhaust mechanism similar to one used in the conventional tungsten CVD method.
Here, in the semiconductor manufacturing process, when a metallic thin film such as tungsten is to be formed with the CVD method, the generation of particles must be suppressed as much as possible in order to stably produce high performance integrated circuits, and so it is necessary in this point of view to prevent the deposition on the back surface of a substrate. Also, in particular, in the case of Cu thin films, the prevention of deposition on the back surface of a substrate becomes further important as compared with tungsten or the like for the following reason. That is, since Cu diffuses in Si at a high rate and greatly affects the performance of Si semiconductors, and the diffusion rate is increased as a substrate temperature rises, the prevention of film adhesion and of spreading of a raw material to the back surface of a substrate during deposition becomes particularly important in the case where the deposition is made at high temperatures (J. Electrochem. Soc., 2258-2260 (1999)).
Several measures, which have been established for preventing the deposition on and adhesion of a raw material gas to the back surface of a substrate in the tungsten CVD method, maybe applied to the Cu-CVD method. Here, mechanisms for preventing a raw material gas from spreading to the back surface of a substrate in conventional tungsten CVD apparatuses will be summarized.
FIG. 5 shows, as a first example, a CVD apparatus disclosed in Japanese Patent Laid-Open No. 7-221024. A raw material gas introduction section 35 and a substrate holder 33 opposed to the section for placing thereon a substrate are arranged in a reduced pressure vessel 31, and a gas emitted from the raw material gas introduction section 35 is decomposed to form a thin film on the substrate 32. Here, the holder 33 is moved up and down by a lift 41, and rises at the time of deposition to lift a ring chuck 34 to bring a surface of the substrate 32 into entirely circumferential contact with a lower, horizontal surface of a tip end 40 of the ring chuck 34, thereby preventing a raw material gas from spreading to the back surface of the substrate. Also, at the time of substrate exchange, the holder 33 descends and the ring chuck 34 is supported by a support member 36.
An unreacted raw material gas and a secondary product gas flow into a chamber 71 from a chamber 70 through an opening 39 formed in the support member 36, and are exhausted outside a vessel via an exhaust port 38. Also, a purge gas introduction pipe 42 is provided in a chamber 72 for preventing the raw material gas and the secondary product gas from flowing toward the chamber 72, and a purge gas having been introduced into the chamber 72 flows into the chamber 70 through a gap between the ring chuck 34 and the support member 36 to be exhausted outside the vessel together with the raw material gas and the like.
The prevention mechanism for raw material gas spreading shown in FIG. 5 is designed to have the ring chuck and a substrate contacting with each other over the entire outer circumference portion of the substrate to prevent the raw material gas spreading, so that a distance of contact portions between the ring chuck and the substrate is significant. Also, with this method, the film deposition will occur at the contact portion from the substrate surface to a tip end of the ring chuck.
Similar constructions are also disclosed in Japanese Patent Laid-Open No. 5-38904, U.S. Pat. Nos. 5,000,113 and 5,094,885.
Also, Japan Patent No. 2603909 discloses, as shown in FIG. 6, a mechanism, in which pins 43 mounted on a lower surface and 1.0 to 1.5 mm from the inner circumference of a vertically moving ring chuck 34 are used to fix a substrate 32 to a holder 33, and a purge gas is blown off to the gap between the ring chuck and the substrate to prevent a raw material gas from spreading to the back surface of the substrate. In this method, in terms of the prevention of the raw material gas spreading, a flow rate of purge gas, a spacing A between the ring chuck and the substrate, determined by the height of the pins, and a distance B, over which the ring chuck covers the substrate, are important. In addition, since the pins are disposed on the outer side of the inner circumference of the ring chuck, the film deposition will not be made on the contact portions where the pins and the substrate contact with each other.
Further, Japanese Patent Laid-Open No. 4-233221 discloses, as shown in FIG. 6, a mechanism, in which a vacuum chuck is used to fix a substrate 32 on a holder 33 and a purge gas from a gas groove 45 is blown to the vicinity of an outer circumference portion of the substrate to prevent a raw material gas from spreading to the back surface of the substrate. In this case, the flow rate of the purge gas is important in preventing spreading of a raw material gas. The space between a chuck groove 44 on the holder 33 and the substrate 32 is exhausted with the use of a separate exhaust system from one for a deposition chamber to provide a pressure difference between the chuck groove 44 and the deposition chamber, thereby fixing the substrate 32.
This method has an advantage that the deposition can be made on the entire surface of the substrate and therefor the chip yield is enhanced to lead to an increase in productivity of semiconductor devices.
However, the CVD apparatus shown in FIG. 5 (Japanese Patent Laid-Open No. 7-221024 involves a problem that particles of Cu are generated due to film peeling-off at the contact portion when the ring chuck is detached from the substrate because the film is formed also on the contact portion of the substrate 32 and the ring chuck 34. When the particles of Cu fall on the holder, they will adhere to a substrate to be subsequently processed to cause Cu contamination.
Also, in order to securely prevent the spreading of a raw material gas, it is necessary to increase a width, over which the ring chuck covers the outer circumference portion of the substrate, and therefore there is caused a problem that the deposition area on the substrate cannot but be reduced.
Further, in the course of examining apparatuses and arrangements being more highly effective in prevention of spreading of a raw material gas, the present inventors have found that the CVD apparatus shown in FIG. 5 involves a significant problem. That is, while there is the need of providing a substrate transfer mechanism in the case of manufacturing apparatuses, it has been found that even if a purge gas is made flow, the prevention effect of raw material gas spreading is greatly lowered when the substrate transfer ports for a substrate transfer arm are provided in an outer side wall and an inner side wall 37 of the chamber 71.
In variously examining the entire construction including mount positions of substrate transfer ports and the like, it has been found that the gas flowing path of a raw material gas, along which the raw material gas is exhausted outside the vessel after it has been introduced into a reduced pressure vessel, greatly affects the extent of spreading of the raw material gas and that the prevention effect of the raw material gas spreading can be enhanced by forming a gas flow in axial symmetry and without stagnation. More specifically, the reason why the provision of substrate transfer ports lowers the prevention effect of raw material gas spreading in the apparatus shown in FIG. 5 is presumably that since the opening 39 cannot be symmetrically provided around the substrate, the gas flow becomes ununiform to cause the stagnation of the raw material gas to permit the raw material gas to spread into the chamber 72, thus causing the contamination on the back surface of the substrate. Also, it is believed that even if a purge gas is introduced into the chamber 72 to flow toward the chamber 70, the above construction makes the flow of the purge gas partial and so an adequate prevention effect cannot be exhibited.
With the second example (Japan Patent No. 2603909), even if a purge gas is made flow through a gap between the substrate 32 and the ring chuck 34, a raw material gas in some cases diffuses to low concentration side against the flow of the purge gas, due to ununiformity in flow rate and the flow of the purge gas.
Besides, since a distance B, over which the ring chuck covers the substrate, is as short as 1.0 to 1.5 mm, the raw material gas may reach the holder 33 in the vicinity of the substrate, and as the number of substrates to be processed increases, the film adhesion occurs on the holder surface, which become responsible for the contamination on the back surface of the substrate.
Also, the substrate 32 is fixed by means of the pins 43, the purge gas is made flow through the gap A determined by the height of the pins, and a predetermined distance between the tip end of the ring chuck and the pins is required so as to eliminate the deposition on the pins, so that the deposition on the entire surface of the substrate is impossible like the first example.
With the third example (Japanese Patent Laid-Open No. 8-233221), the sealing between the substrate and the holder 33 is made by simple contact with the vacuum chuck and the atmospheric gas near the circumference of the substrate is sucked by the vacuum chuck, so that a raw material gas existing near the substrate penetrates into the back surface of the substrate to cause contamination on the back surface of the substrate. Also, this method involves a problem that the application to the deposition at low pressures of 1.5 kPa or less is impossible because a pressure difference between deposition pressure and pressure in the chuck groove 44 is made use of for chucking the substrate.
In this manner, measures employed in conventional tungsten CVD apparatuses, respectively, have advantages and disadvantages and so are not entitled to be adequate in terms of yield rate, chip yield and stable productivity, so that a mechanism is desired, which is excellent in preventing adhesion of a raw material gas to the back surface of a substrate. In particular, with CVD apparatuses used in formation of Cu thin films for wiring of semiconductor circuits, since integrated circuits are deteriorated in performance if even a minute amount of raw material gas adheres to the back surface of a substrate as described above, a more strict adhesion preventing mechanism has been demanded as compared with tungsten and the like. That is, it has been said that it is necessary to limit Cu contamination on the back surface of a substrate, to for example, 1xc3x971013 cmxe2x88x922 or less (J. Electrochem. Soc., 2258-2260 (1999)).
Under the circumstances described above, the present invention has its object to solve problems of prior art apparatuses and to provide a CVD apparatus having a high productivity, involving less contamination on the back surface of a substrate and having a high yield.
Further, it is an object of the invention to provide a CVD apparatus for formation of Cu thin films applicable to semiconductor integrated circuits, which will be further promoted in high integration and high performance in the future.
In order to solve the problems of the prior art and attain the above-mentioned objects, the present inventors have made various, fundamental investigations on the relationship between internal constructions of a reduced pressure vessel, gas flows, substrate fixing methods or the like and the contamination on the back surface of a substrate and as a result accomplished the invention shown below.
That is, a CVD apparatus of the present invention for forming a thin film including at least one of constituent elements of a raw material gas on a substrate by placing the substrate on a heating holder provided in a reduced pressure vessel, fixing the substrate by means of a ring chuck having the function of preventing the raw material gas and a secondary product gas from spreading to the back surface of the substrate, and introducing the raw material gas from a gas introducing section provided to be opposed to the substrate, is characterized by a support member provided on side walls of the reduced pressure vessel to hold the ring chuck, an interior of the reduced pressure vessel being divided into upper and lower portions by the ring chuck, the support member and the substrate, an inner wall provided to connect a roof plate of the vessel and the support member to each other and to further divide the upper portion into a deposition chamber and an exhaust chamber, a transfer chamber provided in the lower portion for substrate transfer, both of the deposition chamber and the exhaust chamber being formed in axial symmetry around the same central axis and communicated to each other by holes provided in the inner wall, and the deposition chamber and the transfer chamber being communicated to each other by a gap formed between the ring chuck and the support member.
In this manner, the interior of the reduced pressure vessel is divided into upper and lower portions, and the deposition chamber and the exhaust chamber are provided at the same horizontal level in the upper portion to be disposed in axial symmetry around the same central axis, whereby gas flows without stagnation can be formed within the deposition chamber and the exhaust chamber. As a result, a raw material gas and a secondary product gas are inhibited from spreading toward the transfer chamber provided in the lower portion, and deposition and adhesion of them on the back surface of the substrate can be suppressed.
Also, a CVD apparatus of the invention is characterized by a support member provided on side walls of the reduced pressure vessel to hold the ring chuck, an interior of the reduced pressure vessel being divided into upper and lower portions by the ring chuck, the support member and the substrate, an inner wall suspended from a roof plate of the vessel toward the ring chuck with a predetermined gap therebetween to further divide the upper portion into a deposition chamber and an exhaust chamber, a transfer chamber provided in the lower portion for substrate transfer, both of the deposition chamber and the exhaust chamber being formed in axial symmetry around the same central axis and communicated to each other by a gap between the inner wall and the ring chuck and/or holes provided in the inner wall, and the deposition chamber and the transfer chamber being communicated to each other by a gap formed between the ring chuck and the support member.
With such arrangement, the purge gas flows directly into the exhaust chamber from the transfer chamber but does not flow into the deposition chamber, so that the flow in the deposition chamber can be made less stagnation to further reduce the amount of a raw material gas and the like entering into the transfer chamber.
Further, a CVD apparatus of the invention for forming a thin film including at least one of constituent elements of a raw material gas on a substrate by placing the substrate on a heating holder provided in a reduced pressure vessel, fixing the substrate by means of a ring chuck having the function of preventing the raw material gas and a secondary product gas from spreading to the back surface of the substrate, and introducing the raw material gas from a gas introducing section provided to be opposed to the substrate, is characterized in that the ring chuck is provided at a lower portion of the inner circumference edge thereof with a tapered portion to hold and fix the substrate on the heating holder, and an outlet for a purge gas is provided on the tapered portion to permit the purge gas to be emitted to an outer circumference portion of the substrate from the outlet.
In this manner, the outer circumference portion of the substrate is held and fixed by the tapered portion of the ring chuck whereby it is possible to surely prevent a raw and a secondary product gas from spreading to the back surface of the substrate. Also, because of line contact between the ring chuck and the substrate, heat conduction from the substrate is suppressed to inhibit the deposition on the ring chuck as well as a contact portion thereof with the substrate. Further, even in the case where the diffusion in very small amount is not allowable as with Cu, it is possible to surely shut off spreading of a raw material gas and a secondary product gas to the back surface by introducing the purge gas to the outer circumference portion of the substrate from the purge gas outlet provided on the tapered portion.
Besides, since a thin film can be formed over substantially the entire surface of the substrate while the spreading of a raw material gas to the back surface is surely shut off, it is possible to enhance the yield of semiconductor chips.